1. Field of the Invention
The present invention relates to improvements in nebulizers for producing mists having small particle sizes.
2. Description of the Background Art
Nebulizers and other mist generators have been made for a wide variety of purposes including therapeutic and diagnostic applications in the medical field, as well as non-medical applications. Therapeutic applications include delivery of medication to the lungs and air passageways of a patient. Diagnostic applications include utilization of an aerosolized radioactive isotope for ventilation of the lungs to enable the production of multiple images of relatively high resolution and contrast to facilitate location of emboli, tumors and the like, and to diagnose other diseases affecting the respiratory track.
Diagnosis of respiratory diseases using radioactive aerosols requires mists having exceedingly small particle sizes in order to avoid excessive deposition or rain-out of the mist particles in the upper respiratory track of the patient, as well as the oral pharynx, the trachea and at airway intersections. To prevent uneven deposition of the mist between the central and peripheral areas of the lung, radioactive aerosols should be delivered to the lung in a substantially uniform manner, and should have a particle size maintained below about 1.2 microns with the major portion of the particles being well below 1 micron.
Nebulizers that produce exceedingly small particle sizes suitable for diagnosis of respiratory diseases are disclosed in commonly owned U.S. Pat. Nos. 4,116,387 and 4,456,179. The nebulizers disclosed in these two patents both have an inverted frusto-conical bottom wall portion forming a liquid reservoir that slopes downwardly and inwardly towards the base of a pressurized gas nozzle. A passageway extends from the base of the nozzle towards the nozzle outlet to draw liquid from the reservoir in response to gas discharged from the nozzle, and thereby form a mist.
While the nebulizers disclosed in the above-referenced U.S. patents produce aerosols having exceedingly small particle sizes, during use, a phenomenon known as "sputtering" may occur prior to complete discharge of liquid from the reservoir. Once "sputtering" begins, the delivery of nebulized liquid is erratic, reducing the uniformity of the delivery of the radioactive aerosol. Accordingly, there remains a need in the art for a nebulizer that provides substantially complete discharge of liquid from the reservoir before "sputtering" occurs.